1. Field of the Invention
The present invention is related to a capacitance detecting type acceleration sensor and a manufacturing method thereof, capable of simultaneously measuring acceleration along either two axes or three axes, applicable to a vibration measurement, a vehicle control, and a motion control.
2. Description of Related Art
As sensors for detecting acceleration applied to a moving object, there are various sorts of sensors such as piezoelectric type sensors, distortion gauge type sensors, magnetic type sensors for using differential transformers, and capacitance type sensors for detecting capacitance changes in capacitors. Very recently, especially, as the acceleration sensors with utilizing the micromachining technique in the semiconductor field, a great attention is paid to the acceleration sensors with using the piezoelectric effect, the electric resistance value of which is varied in response to external mechanical force, and the acceleration sensor for calculating the acceleration by detecting changes in the capacitors. These sensors own various merits such as compactness of devices, mass-productivity, higher precision, and higher reliability. In particular, the acceleration sensor for electrically detecting the acceleration based on the changes in the capacitance value of the capacitor is disclosed in, for example, J-P-A 8-32090 (J-P-A: Japanese Patent unexamined publication.
FIG. 9 is an explanatory diagram for showing an example of the conventional capacitance type acceleration sensor described in J-P-A 8-32090. FIG. 9(a) is a plan view, and FIG. 9(b) is a sectional view. The variable electrode 1 corresponding to the silicon mass body is supported via the beam 3 by an anchor portion 2. The fixed electrodes 4 and 5b are formed with defining a constant space on the side surface of this mass body. The capacitors 10 and 11 are formed by the mass body 1 and the fixed electrodes 4 and 5b. As seen from the A--A sectional view of FIG. 9, the sensor structure containing these auxiliary supporting unit 7 is jointed to the glass substrate 8a and the glass substrate 9b by the anode jointing method, and the region used to form the capacitors is hermetically sealed. These capacitors 10 and 11 constitute the sensor element 12. When inertial force caused by acceleration is exerted along the x-direction of the mass body 1, the mass body 1 is displaced along the x-direction. One electric capacitance defined between the mass body 1 and the fixed electrodes 4, 5 is increased (C.times.1=C+.DELTA.C) by the displacement, whereas the other capacitance defined between the mass body 1 and the fixed electrodes 4, 5 is decreased (C.times.2=C-.DELTA.C) by the displacement.
This capacitance change is converted into the voltage output by the IC-formed detecting chip (ASIC), so that this acceleration can be derived as the voltage output. This IC-formed detecting chip owns the capacitance-to-voltage converting circuit having: EQU Vout=C.times.1/(C.times.1+C.times.2).multidot.Vs
In this formula, symbol "Vout" indicates the voltage output, and symbol "Vs" shows the input voltage.
In the case that the above-described acceleration sensor, this acceleration sensor is limited to the acceleration measurement of the one axial direction (x direction). Accordingly, when the acceleration along the two axial directions, or the three axial directions is measured, two sets of the sensor elements and of the ASICs are required, so that the dimension of the package for storing the sensor elements and the ASICs is increased. Therefore, there is a problem that the manufacturing cost is increased.